1. Field of the Invention
The present invention relates to a data communication apparatus, method and system and to a storage medium, and more particularly to techniques of remotely controlling a desired function of an apparatus connected in a network via which information data (including image data and the like) and command data are transferred at high speed.
2. Related Background Art
Conventional peripheral apparatus of a personal computer (hereinafter described as PC) are hard disk drives and printers. These peripheral apparatus are connected to PC via a dedicated input/output interface or a general digital interface such as SCSI (small computer system interface).
Recently, AV (audio/visual) apparatus such as digital cameras and digital video cameras dealing with still and moving images have been paid attention as other types of PC peripheral apparatus. Still and moving images handled with an AV apparatus have a very large amount of data, and a conventional dedicated interface or SCSI interface is associated with the following problems: (a) low data transfer rate; (b) limit in connection methods; (c) small number of connectable peripheral apparatus and their types; (d) thick cable; (e) high cost; and the like.
IEEE 1394-1995 specifications are known as one type of next generation high speed and high performance digital interface techniques capable of solving such problems. A digital interface in conformity with the IEEE 1394-1995 specifications (hereinafter called a 1394 interface) has the following characteristic functions:                (1) high data transfer rate;        (2) support for real time data transfer mode (i.e., isochronous transfer mode);        (3) connection structure (topology) with high degree of freedom; and        (4) support for plug & play function and hot swapping function.        
A network configured by conventional 1394 interfaces (hereinafter called a 1394 serial bus system) is, however, associated with the following problems.
In the conventional 1394 serial bus system, when an apparatus remotely controls one of a plurality of functions supported by a remote apparatus, the apparatus cannot know the operable or controllable range of the function although it can transmit a control signal for controlling the function. Therefore, in order to know the operable range of the function, a user is required to actually operate the function in order to know to which range the function can be operated and from which range the function cannot be operated. There are therefore problems such as cumbersome range detection procedure, considerable process operation delay, lowered communication efficiency, poor user operability, and the like.
Also in a conventional 1394 serial bus system, there is another problem that an apparatus cannot inquire some remotely operable functions collectively among a plurality of functions supported by a remote apparatus. Because of this problem, each apparatus is required to inquire whether each function supported by a remote apparatus can be remotely operated. There are therefore problems such as cumbersome inquiry procedure, considerable process operation delay, lowered communication efficiency, poor user operability, and the like.